Today there are a wide variety of computer and telecommunications devices, such as personal computers (PCs), mobile telephones, and personal digital assistants (PDAs), that need to share information with each other. Generally, this information is communicated from a sending device to a receiving device.
The sending device generally has the data in the initial form of a set of digital words (sets of ones and zeros). In the sending device, a transmitter circuit converts each word into a sequence of electrical pulses, and transmits the sequence of pulses through a cable, circuit board, or other medium to the receiving device. The receiving device includes a receiver circuit that identifies each of the pulses in the signal as a one or zero, enabling it to reconstruct the original digital words.
A key component in both the transmitter and the receiver is a voltage-controlled oscillator, a circuit that produces a signal that varies back and forth between two voltage levels at a frequency based on an input control voltage. The transmitter uses a VCO to place digital information into a high-frequency carrier signal, and the receiver uses a VCO to separate the digital information from the high-frequency carrier signal. Thus, voltage-controlled oscillators (VCOs) are critical building blocks in high-performance communication systems. The ever-increasing demand for bandwidth places very stringent frequency, power, and noise requirements on such systems.